All About Kitchen Venting

A range hood is more than a mechanism to remove cooking odors; it’s an important component in a kitchen’s decor. A sleek, well-designed model makes a bold statement: that the resident chef is no slouch. But beyond putting on culinary airs, a range hood is something akin to a life-support system for your kitchen.

In days gone by, ventilating the kitchen meant opening a window. Today, however, houses are being built increasingly airtight, central air is ubiquitous, and windows remain closed most of the year, making mechanical ventilation a necessity. An effective range hood will exhaust excess heat, humidity, cooking odors and fumes from household chemicals. The best models will also trap grease to help keep the kitchen clean. All these features make the range hood an integral part of a home’s indoor air-quality system, improving safety and hygiene.

Modern range hoods offer a wide variety of options in terms of style, function and capacity. Here’s what you need to know when selecting the right model for your kitchen.

Recirculating vs. outdoor-venting
An effective ventilation system exhausts air outside. Low-end recirculating hoods, which do not have outdoor venting, may filter grease and odors, but they won’t remove humidity and chemical pollutants. Many also make a lot of noise and do little to trap odors and grease. “If an outside-ducted range hood is impractical, consider supplementing the range hood with a central ventilator similar to a bath fan that does vent to the outdoors,” advises James Lyon, a professional engineer with Newport Partners. Keep in mind that building codes require any fan within a 45-degree angle of the cooktop to have a grease trap.

If you must use a recirculating hood, look for a model with a good aluminum-screen grease trap that you can put in the dishwasher and the largest charcoal-bed filter available for smoke and odors. Some models have a combination of baffle and mesh grease filters. The baffles work well when the fan runs at high speed; the mesh is for low speed.

Recirculating fans that work
If you can’t exhaust the kitchen fan through ducts to the outdoors, choose a recirculating fan with the best filters. A non-ducted kitchen fan should include an aluminum-screen grease trap that you can put in the dishwasher and a charcoal-bed filter for smoke and odors. Some range hoods can be connected to an accessory recirculating kit (above) that features additional filters.

An outdoor-vented range hood is always the best choice, but for it to be effective, proper installation is essential (see “Kitchen Vent-Hood Installation,” in PDF below). A too-narrow duct will detract from the hood’s performance; a duct that is too wide may reduce air velocity, resulting in grease deposits along the pipe, says Lyon. The duct should match the hood’s port size and follow a direct path to the exterior, avoiding sharp angles. Never use corrugated pipe; grease will build up in the grooves and could catch on fire.

Canopy choices
When choosing a hood, you’ll need to select the right size canopy (the visible portion of the hood that captures air). The canopy should be as wide as the cooktop and at least 18 in. deep but preferably 24 to 27 in. Extra depth matters more than width, says Brian Wellnitz, a kitchen ventilation spokesman for Broan. “The hood should cover all the back burners and at least three-quarters of the front burners,” he says. The canopy should be 18 to 30 in. above the cooktop. Some kitchen designers like to add a few inches to show off backsplash tile or provide a more comfortable view of the stove for a tall cook, but if you set the hood higher than 30 in., you will need a stronger fan.

Fan sizes
The next consideration is horsepower. In the world of hoods, brawn is measured by how many cubic feet of air per minute (cfm) the hood’s fan can exhaust. The Home Ventilation Institute (a manufacturers’ trade association) recommends a range hood with a fan capacity of 40 to 50 cfm per linear foot of range (about 120 to 150 cfm for a standard 30-in. unit), but the engineers we spoke to recommend a minimum of 160 cfm. “A fan’s functional capacity is often much lower than the manufacturer’s rating,” explains Steve Easley, a building science consultant at S. Easley & Associates Inc.

For a large, multiburner, commercial-style range, you should always follow the stove manufacturer’s recommendations about fan size. The manufacturer bases recommendations on a combination of factors including the stove’s heat output, the location of the hood and the length of the duct between the hood and the outdoor exhaust outlet.

Keep in mind that bigger isn’t always better. “Bigger fans consume more electricity, and they can create a dangerous condition called back drafting,” explains Easley. This occurs when the suction of a powerful fan creates negative pressure in the home and interferes with the exhaust ventilation of combustion devices. (Safety note: When installing a high-capacity exhaust system of 900 cfm or more, hire an energy-audit contractor to verify that the fan is not creating negative pressure. Experts recommend coupling any large range hood with a hard-wired carbon-monoxide detector as a precaution.)

Fan motors may be housed within the fan, on an exterior wall or in line on a duct (see “Fan Basics,” in PDF below). When the motor is housed in the hood or within earshot, the sound characteristics of the fan become an important consideration because loud fans are irritating and we tend to shut them off. The quietest location for the fan motor is outside, but harsh weather can make this impractical. Look for a fan with a quiet motor — a good indicator of the quality and efficiency of the fan, as quieter motors require better components and run more efficiently.

Over-the-range microwave
You’ll get better ventilation from a dedicated vent hood than from an over-the-range (OTR) microwave with a built-in vent fan. But if space is limited, an OTR microwave that is ducted to the outdoors may be the solution, especially if you don’t do a lot of high-heat cooking on your stove. Look for a model, such as the GE Profile Advantum 120, that features washable filters and a fan that moves at least 300 cfm to help compensate for the small capture area.

Overhead or downdraft
Because hot air rises, the standard configuration of an overhead hood placed against a wall typically works best. But sometimes the stove’s location (for example, in a kitchen island) requires a downdraft model or a freestanding hood. These hoods draw significantly more air to compensate for cross currents. When choosing a hood that will be located over a kitchen island, you should multiply the cfm requirement of a conventional hood by 1.5, says the Heating and Ventilation Institute.

Given the variety of options available, you can find the perfect range hood for your kitchen. Shop around for a model that will quietly remove moisture and indoor pollutants, light up your work area, operate energy-efficiently and look great.

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